CMenu

右键菜单

void CChildView::OnContextMenu(CWnd* /*pWnd*/, CPoint point)
{
    if (point.x == -1 && point.y == -1)
    {
        //keystroke invocation
        CRect rect;
        GetClientRect(rect);
        ClientToScreen(rect);

        point = rect.TopLeft();
        point.Offset(5, 5);
    }

    CMenu menu;
    VERIFY(menu.LoadMenu(IDR_RMENU));

    CMenu* pPopup = menu.GetSubMenu(0);
    ASSERT(pPopup != NULL);
    CWnd* pWndPopupOwner = this;

    while (pWndPopupOwner->GetStyle() & WS_CHILD)
        pWndPopupOwner = pWndPopupOwner->GetParent();

    pPopup->TrackPopupMenu(TPM_LEFTALIGN | TPM_RIGHTBUTTON, point.x, point.y,
        pWndPopupOwner);
}

显示，隐藏菜单

// hide
this->SetMenu(NULL);
this->DrawMenuBar();

// show 
CMenu m_Menu;
m_Menu.LoadMenuW(IDR_MENU1);
SetMenu(&m_Menu);
this->DrawMenuBar();

修改系统菜单

已经有代码了，直接添加自定义菜单就可以了。
需要在 Resource.h 里面手动添加一个菜单 ID #define IDM_SYSCOMMAND_CUSTOM 32771
别忘了修改一下下面的下一个可用 id 序号，

// Next default values for new objects
// 
#ifdef APSTUDIO_INVOKED
#ifndef APSTUDIO_READONLY_SYMBOLS
#define _APS_NEXT_RESOURCE_VALUE        135
#define _APS_NEXT_COMMAND_VALUE         32772
#define _APS_NEXT_CONTROL_VALUE         1005
#define _APS_NEXT_SYMED_VALUE           104
#endif
#endif

BOOL CMRLGaugerDlg::OnInitDialog()
{
	CDialogEx::OnInitDialog();
    ...
    
	CMenu* pSysMenu = GetSystemMenu(FALSE);
	if (pSysMenu != nullptr)
	{
		BOOL bNameValid;
		CString strAboutMenu;
		bNameValid = strAboutMenu.LoadString(IDS_ABOUTBOX);
		ASSERT(bNameValid);
		if (!strAboutMenu.IsEmpty())
		{
			pSysMenu->AppendMenu(MF_SEPARATOR);
			pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
		}
		// 设置系统菜单
        // 设置系统菜单 第一个参数可以设置选中，未选中 MF_UNCHECKED 
		// m_pSysMenu->AppendMenu(MF_CHECKED, IDM_SYSCOMMAND_CUSTOM, _T("Custom Menu"));
	//	pSysMenu->AppendMenu(0, IDM_SYSCOMMAND_CUSTOM, _T("Custom Menu"));
		pSysMenu->InsertMenuW(0,MF_CHECKED| MF_BYPOSITION, IDM_SYSCOMMAND_CUSTOM, _T("菜单栏"));

	}
    ...


void CMRLGaugerDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
	if ((nID & 0xFFF0) == IDM_ABOUTBOX)
	{
		CAboutDlg dlgAbout;
		dlgAbout.DoModal();
	}else if (nID == IDM_SYSCOMMAND_CUSTOM)
	{
		// toggle menu 
		if (MF_CHECKED == m_pSysMenu->GetMenuState(IDM_SYSCOMMAND_CUSTOM,MF_BYCOMMAND))
		{
			m_pSysMenu->CheckMenuItem(IDM_SYSCOMMAND_CUSTOM, MF_UNCHECKED);
		}
		else
		{
			m_pSysMenu->CheckMenuItem(IDM_SYSCOMMAND_CUSTOM, MF_CHECKED);
		}
		
	}
	else
	{
		CDialogEx::OnSysCommand(nID, lParam);
	}
}